This invention relates to a system for interfolding sheets, such as paper toweling, and more particularly to an interfolding system which is capable of forming a discontinuity in a stack of interfolded sheets to enable the stack to be separated at predetermined locations according to a desired sheet count.
Conventional sheet interfolding systems sever a pair of webs into sheets which are then supplied to a nip formed by a pair of folding rolls. The sheets are supplied to the folding rolls in two staggered streams, and the folding rolls are operable to interfold the sheets and to discharge the interfolded sheets to form a stack. Various mechanisms are known to separate the stack to a desired sheet count downstream of the folding rolls. Examples of such mechanisms are disclosed in Hathaway U.S. Pat. No. 4,721,295 issued Jan. 26, 1988 and Couturier U.S. Pat. No. 4,770,402 issued Sep. 13, 1988. The '402 patent discloses counting fingers at the discharge of the folding rolls which count the number of sheets discharged to a vertically movable table. When a predetermined count is attained, a pair of fingers are moved into the discharged path of the interfolded sheets. One of the fingers engages the top of the stack and is moved downwardly along with the table to separate the stack and enable it to be discharged from the table. The other finger supports the sheets discharged from the folding rolls while the separated stack is being discharged from the table, and the table is then again moved upwardly to engage the bottom of the subsequent stack, and the process is repeated. The Hathaway '295 patent shows a generally similar system. While systems of this type are understood to operate in a generally satisfactory manner, they entail certain drawbacks such as the complexity and cost associated with the vertically movable tables and fingers and the mechanisms for inserting the fingers into the discharge area of the folding rolls. Further, since the stack of interfolded sheets is continuous, systems of this type must provide sufficient vertical movement to completely separate the interfolded panels from each other underneath the folding rolls.
Stemmler U.S. Pat. No. 5,088,707 discloses a system for forming a gap in a stream of sheets discharged from a pair of folding rolls. The '707 patent contemplates a storage roll located adjacent one of the folding rolls, which is operable to remove a sheet from one of the folding rolls and to place the removed sheet onto the successive sheet. In this manner, a gap is formed in the supply of sheets from one of the webs, and a double sheet is interfolded adjacent the gap. The gap facilitates separation of the stack after discharge from the folding rolls, since vertical movement of the stack is not required in order to separate the panels of the interfolded sheets. While this solution eliminates the need for the complicated counting fingers and alternating stack supporting mechanisms disclosed in the '402 and '295 patents, it also is somewhat disadvantageous in that the stack includes a double folded sheet, which results in the stack having two sheets at either its top or bottom which will be obtained when the stack is cut into length and ultimately placed into a dispenser. Further, the '707 patent discloses removal of a sheet from a folding roll and subsequently depositing the sheet back onto the successive sheet while on the folding roll, which requires modifications to the folding roll and involves the possibility that the removed sheet may be placed out of alignment or registration with the successive sheet when the removed sheet is placed back onto the folding roll.
It is an object of the present invention to provide a simplified system and method for creating a discontinuity in a stack of interfolded sheets. It is a further object of the invention to provide such a system and method which requires no interaction with the folding rolls. Yet another object of the invention is to provide such a system and method which eliminates a double sheet at the top or bottom of a stack, and which does not involve the difficulties associated with removing a sheet from the stream and subsequently replacing the sheet in the stream. A still further object of the invention is to provide such a system and method which is relatively simple in its components and operation and which involves modification of relatively few components of an existing interfolding system.
In accordance with one aspect of the invention, a sheet interfolding system for forming a stack of interfolded sheets from a pair of webs includes a pair of bed rolls to which the pair of webs are supplied and a severing arrangement which cooperates with each bed roll to sever each web into a series of sheets. A pair of folding rolls are arranged to receive the sheets from the pair of bed rolls and to interfold the sheets to form a stack of interfolded sheets at a discharged defined by the folding rolls. The sheets follow a supply path between the bed rolls and the folding rolls. A selectively operable gap forming arrangement is located upstream of the folding rolls, and is operable to selectively move at least the leading portion of one sheet out of the supply path and to move a trailing portion of the same sheet downstream in the supply path to form a gap in the supply of sheets from one of the bed rolls. The leading portion of the sheet is subsequently returned to the supply path upstream of the gap. The gap in the supply of sheets is operable to create a discontinuity in the stack of interfolded sheets to facilitate separation of a portion of the stack from the remainder of the stack after discharge from the folding rolls. The selectively operable gap forming arrangement is preferably in the form of a pair of oppositely rotating rolls which define a nip through which a stream of sheets from one of the bed rolls passes upstream of the folding rolls. The leading portion of the at least one sheet is moved out of the supply path by engagement of the leading portion of the sheet downstream of the nip with a first one of the pair of rolls. A second one of the pair of rolls is operable to advance a trailing portion of the sheet through the nip while the leading portion of the sheet is engaged with the first roll. In a preferred embodiment, the second roll is in the form of a bed roll, and the severing arrangement is in a form of a knife roll which cooperates with the bed roll to sever the web into sheets. The pair of rolls are preferably operable to fold the sheet onto itself. To accomplish this, the leading portion of the sheet is engaged with the first roll downstream of the nip while the trailing portion of the sheet is advanced through the nip by rotation of the second roll. After the trailing portion of the sheet has at least partially passed through the nip, engagement of the leading portion of the sheet with the first roll is released while rotation of the second roll is continued. Upon continued rotation of the second roll, the leading portion of the sheet is folded back onto the trailing portion, to form a folded sheet which is located immediately downstream of the gap formed by removal of the leading portion of the sheet from the supply path. The folded sheet is then discharged and interfolded with the remaining sheets, and the gap functions to form a discontinuity in the stack of sheets discharged from the folding rolls.
The invention further contemplates a method of creating a discontinuity in a stack of interfolded sheets formed at the discharge of a pair of folding rolls. The method contemplates forming a gap in a first stream of sheets which is supplied to the folding rolls along with a second stream of sheets. The gap in the first stream of sheets is formed upstream of the folding rolls by folding at least one of the sheets in the first stream of sheets onto itself to create a folded sheet which defines the gap in the first stream of sheets. Simultaneously, the supply of sheets in the second stream of sheets is maintained, and the first and second streams of sheets are supplied to the folding rolls. As noted above, the gap functions to form a discontinuity in the stack of interfolded sheets discharged from the folding rolls. The step of folding the sheet is preferably carried out on one of the bed rolls by lifting a leading portion of the sheet off of the bed roll while maintaining a trailing portion of the sheet on the bed roll. The bed roll is rotated to advance the trailing portion of the sheet relative to the leading portion, and the leading portion of the sheet is then returned to the bed roll so as to overlie the trailing portion of the sheet. In a preferred form, the step of lifting the leading portion of the sheet off of the bed roll is carried out by positioning a separating roll adjacent the bed roll and selectively operating the separating roll to engage the leading portion of the sheet with the separating roll.
In one form, the leading portion of the sheet is engaged with the separating roll by supplying suction to a surface of the separating roll located adjacent the bed roll and subsequently rotating the separating roll and the bed roll in opposite directions. The trailing portion of the sheet may be maintained in engagement with the bed roll by supplying suction to a surface of the bed roll which underlies the trailing portion of the sheet. The leading portion of the sheet is subsequently returned to the bed roll after the separating roll has attained a predetermined rotational position relative to the bed roll by cutting off the supply of suction to the surface of the separating roll.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.